It is well known in the art that aluminum alkoxide structures are very complex. Aluminum alkoxides having the structural formula are referred to as aluminum tri-alkoxides and are useful components of products where tri-functionally (i.e. three reactive sites) is desired. The monomeric structure, i.e., Structure A, is used herein for ease of identification, although in actual occurrence there may be two, three, four or more of these aluminum tri-alkoxide molecules joined together by intermolecular forces to form corresponding dimeric, trimeric, tetrameric, or higher polymeric forms of such compounds. Whether the aluminum tri-alkoxide is in the monomeric, dimeric, trimeric, tetrameric, or higher polymeric form, it is always referred to as tri-functional because there are three reactive OR groups per atom of aluminum.
Aluminum tri-alkoxides react with carboxylic acids, carboxylic acid anhydrides, and hydroxyl groups and carboxyl groups present in other compounds. Hence, the usefulness of aluminum tri-alkoxides has been well established. For example, aluminum tri-alkoxide compounds may be used to prepare aluminum complex greases and soaps.
Aluminum tri-alkoxides, particularly aluminum tri-isopropoxide and aluminum tri-secondary butoxide, are also employed commercially in the manufacture of printing ink vehicles. The aluminum tri-alkoxides react with resins in the printing ink vehicles to modify the rheology of the vehicles. Printing ink vehicles that have been made and modified rehologically with aluminum tri-alkoxides are subsequently combined with color dispersions or pigments and solvents to produce the final printing ink. Printing inks made with vehicles comprising aluminum tri-alkoxides exhibit improved performance on high-speed printing presses.
Aluminum tri-isopropoxide is commercially available only in the form of a solid tetramer. The solid form of aluminum tri-isopropoxide is reactive with atmospheric moisture, which greatly reduces its reactivity with other reactive groups. Moreover, aluminum tri-isopropoxide, typically, is sold as a finely divided powder. The high surface area of the powder increases the likelihood of moisture contact, thereby reducing the activity and usefulness of aluminum tri-isopropoxide. Also, the solid tetrameric form of aluminum tri-isopropoxide has poor solubility in aliphatic solvents such as ink oils and is, in many cases, soluble only at elevated temperatures.
A problem with using aluminum tri-isopropoxide for rheology control in printing ink vehicles is that this aluminum tri-alkoxide releases isopropyl alcohol as a byproduct of the thickening reaction that occurs during manufacture of the printing ink vehicle. The alcohol boils up during the thickening reaction and must be condensed or scrubbed out of overhead streams to prevent it from discharging into the atmosphere. Resulting condensates and scrubbing solutions must be disposed of as hazardous waste.
Aluminum tri-secondary butoxide remains liquid in storage at ambient temperatures and is often used in place of aluminum tri-isopropoxide where a tri-functional aluminum alkoxide is desired. However, aluminum tri-secondary butoxide presents its own environmental and industrial hygiene problems. Aluminum tri-secondary butoxide typically exhibits a flash point below 100° F., which renders this aluminum tri-alkoxide subject to special handling and labeling regulations. Many manufacturers of products that include aluminum tri-alkoxides are located in areas where materials subject to such special regulations are either prohibited or subject to higher insurance premiums.
A problem with using aluminum tri-secondary butoxide in printing ink vehicles and aluminum greases is that secondary butyl alcohol is released when this aluminum tri-alkoxide is used during the manufacture of these products. Disposal of this by-product is subject to strict regulations.
U.S. Pat. No. 4,525,307 relates to a process for making modified aluminum tri-alkoxides. A higher alcohol is substituted for isopropyl alcohol in molar amounts of 0.5 or less. The modified aluminum tri-alkoxides are disclosed as having improved stability, solubility in hydrocarbon solvents and flash point compared to unmodified aluminum isopropoxide while retaining high reactivity. However, these modified aluminum tri-alkoxides still release byproduct isopropyl alcohol when used in the manufacture of printing ink vehicles.
Thus, it would be desirable to have additional aluminum tri-alkoxides that have a high aluminum content and exhibit good solubility in hydrocarbon solvents. It would also be desirable to have aluminum tri-alkoxides that exhibit high flash points. Alumunim tri-alkoxides that exhibit excellent reactivity with resins in printing ink vehicles and that do not evolve volatile alcohol byproducts during the manufacture of printing ink vehicles or aluminum complex greases are especially desirable.